Generally, thermal cycling causes frequent and repeated stress which in layered structures leads to cracks due to, for example, fatigue. Temperature cycling, therefore, is a material factor in causing failure in layered structures.
In semiconductor device packages, temperature cycling causes failures in die-underfill bonding, underfill-substrate bonding, solder bump attachment and passivation layers among other areas. This reduces the reliability of the package. It is, therefore, desirable to provide a means to reduce failure caused by temperature cycling.
Referring now to the drawings, in which like reference numerals refer to like elements, there is shown in FIGS. 1 and 2 a semiconductor package 5 that is fully described in U.S. patent application Ser. No. 09/819,774, filed Mar. 28, 2001 which is assigned to the assignee of the present application and incorporated herein by reference. FIGS. 1 and 2 show that semiconductor package 5 includes MOSFET 10 inside cup-shaped can 12 which functions as a drain clip. Can 12 is preferably made from a copper alloy and is silver-plated. Can 12 has internal dimensions that are greater than those of MOSFET 10; thus MOSFET 10 is readily received in the interior of can 12. The drain contact of MOSFET 10 is connected to the bottom of can 12 by a layer of silver-loaded conductive epoxy 14. A ring of low stress high adhesion epoxy 16 is applied around the edges of MOSFET 10 to seal and add extra structural strength to the package. Source contact 18 and gate contact 20 of MOSFET 10, which are disposed on a surface of MOSFET 10 opposing its drain contact, are exposed as shown in FIG. 1. Can 12 includes two rows of projections 22 disposed on two of its opposing edges. Projections are provided to make electrical contact with respective lands on a circuit board (not shown), such as an Insulated Metal Substrate or an ordinary circuit board, thereby electrically connecting the drain of MOSFET 10 to its place within a circuit. As shown in FIG. 1, source contact 18 of MOSFET 10 is flush with the contact surfaces of projections 22 of can 12. Therefore, source contact 18 and gate contact 20 of MOSFET 10 will be flush with the surface of the circuit board when package 5 is mounted thereon.
The above-described package is subject to possible failure due to temperature cycling, as described above. It is desirable, therefore, to produce a package design having a similar structure as described above, such that substrate failure caused by thermal cycling is reduced.